DISSOCIATION OF STRONG ELECTROLYTES 111 



up by careful investigations.' Our presentation of this subject 

 is but a preliminary attempt, and there is much in it that still awaits 

 ultimate solution. The perusal of this section of our book then 

 cannot yet yield the degree of satisfaction to be obtained from a well 

 established chapter of a natural science. 



The peculiarity of the strong electrolytes first became evident in 

 those apparent deviations from the mass law which were found in 

 their dissociation. For the purpose of introducing our problem let 

 us consider the determination of the dissociation constant of KCl, 

 which by the mass law is defined as 



[KCl] 

 k = 



[K+] [C1-] 



The method of estimating this constant k appears to be simple at 

 first sight. All one needs is to determine the degree of dissociation 

 in KCl solutions of various concentrations. If this is designated as 

 a, then 



k = , X c 



1 — a 



where c is the total concentration KCl, this being Ostwald's dilution 

 law which has rendered such excellent service in the estimation of 

 dissociation constants of the weak electrolytes. Of the different 

 ways for the determination of the degree of dissociation the con- 

 ductivity method was alwaj^s considered the best. This method is 

 based on the following assumptions: (1) The conductivity of a solu- 

 tion of an electrolyte is a purely additive function of the conductivi- 

 ties of its component ions. (2) Every individual ionic species 

 possesses within wide limits a constant molar conductivity. The 

 latter is proportional to the motility of the ionic species (assumed to 

 be constant), i.e., the rate of migration imparted to an ion by the 

 action of a homogeneous electric field of unit strength. From these 

 assumptions we derive the following expression which serves as a 

 measure of the degree of dissociation, a, 



A 



a = — 



00 



* For the earlier accounts see K. Drucker, Anomalie der starken Electrolyte. 

 Stuttgart, 1905. 



